Retinoblastoma Susceptibility gene (RB) is the first identified cancer suppressor gene. It has been mapped to chromosome 13q14 and shown that tumorigenicity of mutant RB genes is achieved through complete loss of RB protein. The RB protein binds DNA and may regulate other genes. In this lab, the genomic organization of the RB gene has been characterized and distinct genetic alterations have been identified in Y79 retinoblastoma cell line. It has also been shown that RB gene defects are not just limited to retinoblastomas, but also are present in subsets of osteosarcoma, synovial sarcoma, and breast cancer. Of interest, subsets of various preleukemic and leukemic disorders have chromosomal changes involving band 13q14. Preleukemic states tend to have only 13q14 defects, whereas leukemic states have 13q14 plus other chromosomal defects. It is likely that the RB gene is involved in these subsets of preleukemia and leukemia. The aims of this study are several fold: 1) to investigate possible RB gene involvement in subsets of preleukemia and leukemia. RB DNA, mRNA, and protein will be analyzed from bone marrow, peripheral blood and leukemia cell lines. 2) to suppress oncogenesis by using retroviral vectors to reintroduce the RB gene into those involved subsets. Normal Rb gene will be coupled to strong promotors and introduced into RB deficient preleukemia/leukemia cells in culture. Parental and transfected cell lines will be assayed for evidence of in vitro differentiation and in vivo loss of tumorigenicity in nude mice. 3) to initiate oncogenesis by inhibiting RB gene function in normal blood precursors using antisense RNA inhibition. Normal marrow stem cell and progenitor cell RB gene will be inactivated by antisense RNA inhibition of RB mRNA. The target cells will then be assayed for transformed phenotype and tumorigenicity. This proposal holds promise for further understanding the mechanisms of recessive oncogenesis and provides a framework for consideration of gene therapy in cancer.